Semiconductor package having dimpled plate interconnections

ABSTRACT

A semiconductor package is disclosed. The package includes a leadframe having drain, source and gate leads, a semiconductor die coupled to the leadframe, the semiconductor die having a plurality of metalized source areas and a metalized gate area, a patterned source connection having a plurality of dimples formed thereon coupling the source lead to the semiconductor die metalized source areas, a patterned gate connection having a dimple formed thereon coupling the gate lead to the semiconductor die metalized gate area, a semiconductor die drain area coupled to the drain lead, and an encapsulant covering at least a portion of the semiconductor die and drain, source and gate leads.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation-in-part application which claimspriority under 35 U.S.C. 120 from Ser. No. 11/226,913 filed on Sep. 13,2005 entitled “Semiconductor Package Having Plate Interconnections”, theentire specification of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to a semiconductor package andmore particularly to a semiconductor package having dimpled plateinterconnections between power semiconductor device source and gatemetalized areas and leadframe source and gate leads.

Semiconductor devices are conventionally connected to leadframe leadsusing either plate interconnections or wire bonding. For example, U.S.Pat. No. 5,821,611 discloses a semiconductor device which comprises afirst lead having a tip formed with an island, a semiconductor chip unitmounted on the island of the first lead by means of a solder layer andhaving a plurality of electrode bumps projecting away from the island,and a plurality of additional leads each of which has a tip electricallyconnected to the electrode bumps via respective solder deposits. Theadditional leads include at least second and third leads. The leads arealloyed to the electrode bumps in a heating furnace and the solder bumpsmay spread during heating and create undesirable shapes.

U.S. Pat. No. 6,040,626 discloses a semiconductor package which employsa mixed connection between a MOSFET top surface comprising a lowresistance plate portion for connecting to a source and a wire bond forconnecting to a gate. Wire bonding may introduce short circuits in thedevice due to device dialectric layer damage during the wire bondingprocess.

A semiconductor package with directly connected leads is disclosed inU.S. Pat. No. 6,249,041. A semiconductor device includes a semiconductorchip with contact areas on the top or bottom surface. A first leadassembly, formed from a semi-rigid sheet of conductive material, has alead assembly contact attached to one of the contact areas of thesemiconductor chip. The first lead assembly also has at least one leadconnected to and extending from the lead assembly contact. A second leadassembly, also formed from a semi-rigid sheet of conductive material,has a lead assembly contact attached to another one of the contact areasof the semiconductor chip. The second lead assembly also has at leastone lead connected to and extending from the lead assembly contact. Anencapsulant encloses the semiconductor chip, the lead assembly contactof the first lead assembly and the lead assembly contact of the secondlead assembly. The semiconductor device has low electrical and thermalresistance contributions from the package due to the direct connectionof the lead assemblies to the chip. The lead assembly contact areas areheld in contact with lead contact areas on the semiconductor chip by anelectrically conductive adhesive layer. The electrically conductiveadhesive layer may be a silver-filled epoxy or polyimide paste or solderbumps. The adhesive layer may be cured in a curing oven, if necessary.The adhesive layer does not include soft solder or solder paste.

Another semiconductor package with directly connected leads is disclosedin U.S. Pat. No. 6,479,888. A MOSFET comprises a plurality of innerleads electrically connected to a surface electrode of a semiconductorpellet having a field effect transistor on a principal surface thereof.The inner leads are mechanically and electrically connected to theprincipal surface by a gate connecting portion and source connectingportions constituted by bumps.

A common problem encountered in the use of patterned plate or clipinterconnections is that the plates or clips may float during solderreflow and result in a misaligned interconnection. In some cases, themisalignment results in a short circuit between the source and gatecontact areas resulting in low assembly yields. Furthermore, it isdifficult to control the required solder volume to prevent this problem.

Another problem resulting from the use of patterned plate or clipinterconnections is the thermal expansion mismatch between the siliconof the semiconductor device and the metal of the patterned plate orclip. The larger the contact area of the patterned plate or clip, thehigher the stress induced by the mismatch, which often results in diecracking. To reduce the stress, a smaller plate or clip may be used.However, the smaller contact area may result in higher resistance.

There is therefore a need in the art for a semiconductor package thatincludes a semiconductor power device connected to leadframe source andgate leadframe contact areas by means of patterned plates that overcomesthe problems of the prior art. There is also a need for a patternedplate interconnection that does not float during solder reflow andensures precise clip placement and location assurance. There is also aneed for a semiconductor package having device metallized areas forrestricting the flow of solder during the soldering process. There isalso a need for a metalized area formed of Ni/Au. There is also a needfor a semiconductor package process that increases throughput andprovides easier assembly process control. There is also a need for asemiconductor package method that provides a soft attachment process ofthe patterned plates onto the semiconductor power device. There is alsoa need for a semiconductor package having an exposed source plate. Thereis also a need for a semiconductor package having reduced electricalresistance. There is a further need for a semiconductor package havingimproved thermal dissipation properties. There is also a need for asemiconductor package having improved mechanical properties.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byproviding a semiconductor device package having plate connectionsbetween leadframe source and gate contact areas and a powersemiconductor power device source and gate metalized areas. The plateconnections include dimples positioned to correspond to the source andgate metalized areas. A portion of the source plate may be exposed toallow for improved thermal dissipation.

In accordance with another aspect of the invention, a semiconductorpackage includes a leadframe having drain, source and gate leads, asemiconductor die coupled to the leadframe, the semiconductor die havinga plurality of metalized source areas and a metalized gate area, apatterned source connection having a plurality of dimples formed thereoncoupling the source lead to the semiconductor die metalized sourceareas, the dimples being positioned for contact with the metalizedsource areas, a patterned gate connection having a dimple formed thereoncoupling the gate lead to the semiconductor die metalized gate area, thedimple being positioned for contact with the metalized gate area, asemiconductor die drain area coupled to the drain lead, and anencapsulant covering at least a portion of the semiconductor die anddrain, source and gate leads.

In accordance with yet another aspect of the invention, a semiconductorpackage includes a leadframe having drain, source and gate leads, asemiconductor die coupled to the leadframe, the semiconductor die havinga plurality of Ni/Au metalized source areas and a Ni/Au metalized gatearea, a patterned source connection having a plurality of dimples formedthereon, the plurality of dimples coupling the source lead to thesemiconductor die metalized source areas in corresponding relationshiptherewith, the patterned source connection being soldered to thesemiconductor die metalized source areas, a patterned gate connectionhaving a dimpled formed thereon, the dimple coupling the gate lead tothe semiconductor die metalized gate area in corresponding relationshiptherewith, the patterned gate connection being soldered to thesemiconductor die metalized gate area, a semiconductor die drain areacoupled to the drain lead, and an encapsulant covering at least aportion of the semiconductor die and drain, source and gate leads.

There has been outlined, rather broadly, the more important features ofthe invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended herein.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of design and to thearrangement of components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other methods and systems for carrying out theseveral purposes of the present invention. It is important, therefore,that the claims be regarded as including such equivalent methods andsystems insofar as they do not depart from the spirit and scope of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic representation of a semiconductor package inaccordance with the invention;

FIG. 2 is a cross sectional view of the semiconductor package of FIG. 1taken along line 2-2 in accordance with the invention;

FIG. 3 is a cross sectional view of the semiconductor package of FIG. 1taken along line 3-3 in accordance with the invention;

FIG. 3A is a schematic representation of a patterned gate connectiondisposed over a metalized gate area in accordance with the invention;

FIG. 3B is a schematic representation of a gate lock in accordance withthe invention;

FIG. 3C is a schematic representation of the semiconductor package ofFIG. 1 showing an alternative metalized gate area in accordance with theinvention;

FIG. 4 is a view in partial section of the semiconductor package of FIG.1 in accordance with the invention;

FIG. 5 is another view in partial section of the semiconductor packageof FIG. 1 in accordance with the invention;

FIG. 6 is a schematic representation of an alternative embodiment of thesemiconductor package in accordance with the invention;

FIG. 7 is a cross sectional view of the semiconductor package of FIG. 6taken along line A-A in accordance with the invention;

FIG. 8 is a cross sectional view of the semiconductor package of FIG. 6taken along line B-B in accordance with the invention;

FIG. 9 is a view in partial section of the semiconductor package of FIG.6 in accordance with the invention;

FIG. 10 is a schematic representation of an alternative embodiment ofthe semiconductor package in accordance with the invention;

FIG. 11 is a cross sectional view of the semiconductor package of FIG.10 taken along line A-A in accordance with the invention;

FIG. 12 is a cross sectional view of the semiconductor package of FIG.10 taken along line B-B in accordance with the invention;

FIG. 13 is a schematic representation of an embodiment of thesemiconductor package having dimpled plate interconnections inaccordance with the invention;

FIG. 14 is a cross sectional view of a dimpled source plate of thesemiconductor package of FIG. 13;

FIG. 15 is a cross sectional view of a dimpled gate plate of thesemiconductor package of FIG. 13;

FIG. 16 is a schematic representation of a semiconductor die inaccordance with the invention;

FIG. 17 is a schematic representation of an alternative embodiment ofthe semiconductor package having dimpled plate interconnections inaccordance with the invention;

FIG. 18 is a cross sectional view of a dimpled source plate of thesemiconductor package of FIG. 17; and

FIG. 19 is a cross sectional view of a dimpled gate plate of thesemiconductor package of FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best modes of carrying outthe invention. The description is not to be taken in a limiting sense,but is made merely for the purpose of illustrating the generalprinciples of the invention, since the scope of the invention is bestdefined by the appended claims.

The present invention generally provides a semiconductor device packagehaving plate connections between leadframe source and gate contact areasand power semiconductor power device metalized source and gate areas.The metalized source and gate areas are preferably Ni/Au plated orsputtered surfaces. The metalized source and gate areas provide forimproved bonding of the plate connections and reduction of overbondingwhich often introduces short circuit problems due to dielectric layerdamage during wire bonding processes. The metalized source and gateareas further eliminate the need for solder bumps and epoxy adhesivelayers as soft solder and solder paste may be used to connect the platesto the metalized source and gate areas.

In a first aspect of the invention and with reference to FIGS. 1-5, asemiconductor package generally designated 100 may include a leadframe105 having a drain contact portion 107, a source contact portion 110 anda gate contact portion 115. A power semiconductor die 120 may have ametalized drain area (not shown) coupled to the drain contact portion107 by solder reflow.

Semiconductor source and gate metalized areas may be formed by Ni/Auplating or sputtering. With reference to FIG. 3A, a gate metalized area160 may be of circular configuration. It has been discovered by theinventors that circular metalized area 160 advantageously restricts theflow of soft solder and solder paste to the confines of the circularmetalized area 160 during solder reflow, thereby reducing the incidenceof undesirable shapes and short circuits.

A patterned source plate 125 may include an exteriorly exposed portion127 and an internal portion 130. Interior portion 130 may be coupled tosource contact portion 110. Exteriorly exposed portion 127 may beexposed outside of an encapsulant 135. Patterned source plate 125 may becoupled to the metalized source area by solder reflow using soft solderor solder paste. Metalized source area may cover a substantial portionof a top surface of the die 120 for improved heat dissipation anddecreased resistance and inductance.

A patterned gate plate 137 may connect the metalized gate area 160 tothe leadframe gate contact area 115. The patterned gate plate 137 mayinclude a hole 165 formed at an end 167 thereof. A locking ball 155 maybe formed during solder reflow to provide mechanical stability to thepatterned gate plate 137 (FIG. 3B). In one aspect of the invention, softsolder may be disposed in the hole 165 and allowed to flow through thehole 165 to the metalized gate area 160 during solder reflow. Metalizedgate area 160 may provide a bonding surface for the solder which limitsthe flow of solder to the circular area.

With reference to FIG. 3C, an alternative metalized gate area 170 isshown including a cross-shaped area.

In accordance with another aspect of the invention, and as shown inFIGS. 6-9, a semiconductor package generally designated 600 may includea leadframe 605 having a drain contact portion 607, a source contactportion 610 and a gate contact portion 615. A power semiconductor die620 may have a metalized drain area (not shown) coupled to the draincontact portion 607 by solder reflow.

Semiconductor source and gate metalized areas may be formed by Ni/Auplating or sputtering. A patterned source plate 625 may include anexteriorly exposed portion 627 and an internal portion 630. Exteriorlyexposed portion 627 may be exposed outside of an encapsulant 635.Patterned source plate 625 may be coupled to the metalized source areaby solder reflow using soft solder or solder paste.

A patterned gate plate 637 may connect the metalized gate area 640 tothe leadframe gate contact area. The patterned gate plate 637 may beconnected to the metalized gate area 640 by solder reflow to providemechanical stability to the patterned gate plate 637.

In another aspect of the invention and with reference to FIGS. 10-12, asemiconductor package generally designated 1000 may include a leadframe1005 having a drain contact portion 1007, a source contact portion 1010and a gate contact portion 1015. A power semiconductor die 1020 may havea metalized drain area (not shown) coupled to the drain contact portion1007 by solder reflow.

Semiconductor source and gate metalized areas may be formed by Ni/Auplating or sputtering. A patterned source plate 1025 may include anexteriorly exposed portion 1027 and an internal portion 1030. Exteriorlyexposed portion 1027 may be exposed outside of an encapsulant 1035.Patterned source plate 1025 may be coupled to the metalized source areaby solder reflow using soft solder or solder paste.

A patterned gate plate 1037 may connect the metalized gate area 1040 tothe leadframe gate contact area. Patterned gate plate 1037 may include ahook portion 1039 for connection to the metalized gate area 1040. Thepatterned gate plate 1037 may be connected to the metalized gate area1040 by solder reflow to provide mechanical stability to the patternedgate plate 1037.

The present invention advantageously employs Ni/Au device patternedsource, drain and gate metalized areas. Ni/Au provides for improvedconnection between the patterned source plates and patterned gate platesand allows for a simplified process of source, drain and gatemetallization in one Ni/Au process to thereby improve processthroughput.

The Ni/Au process provides for a Ni layer on the metal areas and a Aulayer to protect the Ni layer. As Ni does not diffuse into the Al metalarea, an inter-metallic layer comprised of Ni/Al provides for a highdensity layer to which the patterned source and gate connections may besoldered.

In another aspect of the invention, and with reference to FIG. 13, FIG.14, FIG. 15, and FIG. 16, a source plate 1300 includes a plurality ofdimples 1310 formed thereon. The dimples 1310 are concave with respectto a top surface 1320 of the source plate 1300 and have bottom surfaces1315 extending beyond a plane of a bottom surface 1330 thereof. A gateplate 1350 includes a dimple 1360 that is concave with respect to a topsurface 1370 of the gate plate 1350 and has a through hole 1365 havingan opening 1367 that extends beyond a plane of a bottom surface 1380thereof.

Source plate dimples 1310 and the gate plate dimple 1360 are positionedand stamped or punched on the source plate 1300 and the gate plate 1350so as to align with source metalized areas 1620 and gate metalized area1630 of semiconductor die 1600 during solder reflow. It has been foundthat the source plate 1300 is not prone to floating due to the number ofdistinct source plate dimples 1310 contacting the source metalized areas1630. Furthermore, the metalized areas advantageously restrict the flowof soft solder and solder paste to the confines of the metalized areasduring solder reflow, thereby reducing the incidence of undesirableshapes and short circuits. The through hole 1367 the gate dimple 1360allows for the formation of locking balls formed during solder reflow toprovide mechanical stability to the gate plate 1350.

In another aspect of the invention, and with reference to FIG. 17, FIG.18, and FIG. 19 a source plate 1700 includes a plurality of dimples 1710formed thereon. The dimples 1710 are concave with respect to a topsurface 1715 of the source plate 1700 and include a through hole 1720having an opening 1725 formed beyond a plane of a bottom surface 1730thereof. A gate plate 1750 includes a dimple 1760 that is concave withrespect to a top surface 1755 of the gate plate 1750 and includes athrough hole 1770 having an opening 1775 formed beyond a plane of abottom surface 1780 thereof.

As in the embodiment shown in FIGS. 13-16, the source dimples 1710 andthe gate dimple 1760 are positioned and stamped or punched on the sourceplate 1700 and the gate plate 1750 so as to align with source metalizedareas 1620 and gate metalized area 1630 of semiconductor die 1600 duringsolder reflow. The through holes 1720 of the source dimples 1710 and thethrough hole 1770 of the gate dimple 1760 allow for the formation oflocking balls formed during solder reflow to provide mechanicalstability to the source and gate plates 1700 and 1750 respectively. Softsolder may be disposed in the source dimples 1710 and the gate dimple1760 and allowed to flow through the through holes 1720 and 1770 to themetalized source areas 1620 and metalized gate area 1630 respectivelyduring solder reflow. Metalized source areas 1620 and metalized gatearea 1630 may provide bonding surfaces for the solder which limits theflow of solder to the metalized areas.

The present invention advantageously provides for patterned source andgate plate connections having dimples positioned to correspond to sourceand gate metalized areas. The dimpled source and gate plates ensure thatthe source and gate plates do not float during solder reflow to therebyensure precise clip placement and location assurance.

It should be understood, of course, that the foregoing relates topreferred embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1. A semiconductor package comprising: a leadframe having drain, sourceand gate leads; a semiconductor die coupled to the leadframe, thesemiconductor die having a plurality of metalized source areas and ametalized gate area; a patterned source connection having a plurality ofdimples formed thereon coupling the source lead to the semiconductor diemetalized source areas, the dimples being positioned for contact withthe metalized source areas; a patterned gate connection having a dimpleformed thereon coupling the gate lead to the semiconductor die metalizedgate area, the dimple being positioned for contact with the metalizedgate area; a semiconductor die drain area coupled to the drain lead; andan encapsulant covering at least a portion of the semiconductor die anddrain, source and gate leads.
 2. The semiconductor package of claim 1,wherein the metalized source areas and the metalized gate area comprisecircular metalized areas insulated by passivation areas.
 3. Thesemiconductor package of claim 1, wherein the plurality of sourcedimples and the gate dimple each comprise a through hole through whichthe patterned source connection and the patterned gate connection aresoldered to respective source metalized areas and gate metalized area.4. The semiconductor package of claim 3, wherein the solder forms a lockat a top portion of the patterned source connections and the patternedgate connection.
 5. The semiconductor package of claim 1, wherein themetalized source areas and the metalized gate area comprise an upperNi/Au layer.
 6. The semiconductor package of claim 1, wherein the drainarea comprises a metalized drain area.
 7. The semiconductor package ofclaim 6, wherein the metalized drain area comprises an upper NI/Aulayer.
 8. The semiconductor package of claim 1, wherein a bottom portionof the drain lead is exposed through the encapsulant.
 9. A semiconductorpackage comprising: a leadframe having drain, source and gate leads; asemiconductor die coupled to the leadframe, the semiconductor die havinga plurality of Ni/Au metalized source areas and a Ni/Au metalized gatearea; a patterned source connection having a plurality of dimples formedthereon, the plurality of dimples coupling the source lead to thesemiconductor die metalized source areas in corresponding relationshiptherewith, the patterned source connection being soldered to thesemiconductor die metalized source areas; a semiconductor die drain areacoupled to the drain lead; and an encapsulant covering at least aportion of the semiconductor die and drain, source and gate leads. 10.The semiconductor package of claim 9, further comprising a patternedgate connection having a dimpled formed thereon, the dimple coupling thegate lead to the semiconductor die metalized gate area in correspondingrelationship therewith, the patterned gate connection being soldered tothe semiconductor die metalized gate area.
 11. The semiconductor packageof claim 9, wherein the plurality of source dimples and the gate dimpleeach comprise a through hole through which the patterned sourceconnection and the patterned gate connection are soldered to respectivesource metalized areas and gate metalized area.
 12. The semiconductorpackage of claim 10, wherein the solder forms a lock at a top portion ofthe patterned source connections and the patterned gate connection.